Aircraft and other passenger transport vehicle seats are often designed to allow passengers to move from a fully seated upright position to a partially or fully reclined position. These seats may allow only a slight backward motion, or they may be seats that are convertible to a bed, i.e., to a substantially flat bed position so that the passenger may lie down. Premium seats for civil aircrafts typically offer a number of various seat positions, from the most upright position to a full flat or a lie flat bed position. In some instances, these seats may also be surrounded by a privacy shell or partition, which allows seat motion and other passenger movement without interrupting the space of the passenger behind. In that case, the seats are usually composed of a fixed base frame, a movable part used as a seat pan, a back rest, and one or more electrical actuators for seat position adjustment. From upright to the bed-like position, the movable part of the seat will move forward or backward, allowing or causing the backrest to recline or raise without interfering with the privacy shell.
The passenger seat belt is typically attached to the movable part of the seat, in order to retain the passenger in any position. It is important for the seat belt to function to both hold the passenger in place during normal activities, such as take-off and landing and normal air turbulence, as well as to safely restrain the passenger in place during extreme turbulence or crash/crash-like conditions.
Airline guidelines generally require that passenger seats must sustain crash conditions when in upright position. The main issue to solve is thus how to transfer the load due to the passenger mass up to the seat attachment point, knowing that the seat deflection should be limited. This has been done previously either using electromagnetic locker pins to secure the movable part of the seat to the base frame in its upright position or using the brake of the actuator to sustain the load. Both solutions add weight and cost to the design. Accordingly, improved seat belts and securing functions are needed.